Not possible to render self-contained render array while a render stack is active

A solution, based on an extensive IRC discussion between Berdir, Fabianx, catch and I.

(Reusing parts of #2364381: Exception thrown in drupal_render() causes an exception during the rendering of exceptions — if this lands first, we'll be able to reduce that other patch to a single hunk; if the other lands first, then this will be reduced to three hunks.)

RTBC - if tests pass, the patch looks great.

Except that we also need tests for the new functionality ...

Same failure as #2364381: Exception thrown in drupal_render() causes an exception during the rendering of exceptions, which I've been totally unable to find the root cause of :(

My theory is that the renderStack needs to be a synthetic service to keep the state when ConfigUIImportTest rebuilds the container.

I _think_ (and am researching that currently) that a static in a class function is working like a static in a function and global and not per instance ...

That is the theory at least.

Thanks for taking the challenge, Berdir!

My theory is correct:

http://php.net/manual/en/language.variables.scope.php#59676

"Static variables in a function are shared across all instances of that class :)."

That means the stack at the moment is kinda "synthetic".

So we can make the service synthetic or push the stack to a static var for now. (or at least re-initialize it from a static:: var when the stack is NULL).

Wow.

Fabianx++
Fabianx++
Fabianx++
Fabianx++
Fabianx++

:)

Making the service synthetic causes this:

wim.leers at wimleers-acquia in ~/Work/drupal-tres on 8.0.x*
$ drush cr
You have requested a synthetic service ("renderer"). The DIC does not know how to construct this service. 

So I went with the other option: a static $stack property.

I can't get ConfigImportAllTest to pass locally, but ConfigImportUITest now does pass. Let's see what testbot says.

Now with tests.

RTBC, looks great!

1. +++ b/core/lib/Drupal/Core/Render/Renderer.php
   @@ -354,6 +343,55 @@ public function render(&$elements, $is_root_call = FALSE) {
      /**
   +   * {@inheritdoc}
   +   */
   +  public function resetStack() {
   +    self::$stack = NULL;
   +  }
   

   I'm not sure that this needs to be public. Discussed with @Wim Leers in IRC and he agreed.

2. +++ b/core/modules/system/src/Tests/Common/RenderTest.php
   @@ -1197,4 +1197,106 @@ public function testDrupalProcessAttached() {
   +    $this->pass('Renderer::renderRoot() may not be called inside of another Renderer::renderRoot() call, this must trigger an exception.');
   ...
   +      $this->fail('No exception triggered.');
   ...
   +      $this->pass('Exception triggered.');
   

   Do you not mean to set a $message here and use in the $this->fail()/$this->pass() later? Same with subsequent assertions in this test... Nice tests though :)

1. resetStack will need to be public for things where the ExceptionSubscriber will need to reset the stack before displaying the Bare HTML Page.

But we can make it protected first and then back public in the other issue. I am fine either way.

#12: I thought the same, but then I realized the other issue could also just use renderPlain()… :) In case that I'm wrongly thinking that'll work, we can indeed just make it public again.

#11.2: Heh, thanks :) I specifically chose not to do that, I find that having too many variables in tests easily becomes cumbersome; just hardcoding strings makes tests more legible, because you don't need to look up what that variable contains. I left that as-is, hope that's okay.

This issue addresses a critical bug and is allowed per https://www.drupal.org/core/beta-changes. Committed 91b4829 and pushed to 8.0.x. Thanks!